Influence of capillary threshold pressure and injection well location on the dynamic CO2 and H2 storage capacity for the deep geological structure

The subject of this study is the analysis of influence of capillary threshold pressure and injection well location on the dynamic CO₂ and H₂ storage capacity for the Lower Jurassic reservoir of the Sierpc structure from central Poland. The results of injection modeling allowed us to compare the amount of CO₂ and H₂ that the considered structure can store safely over a given time interval. The modeling was performed using a single well for 30 different locations, considering that the minimum capillary pressure of the cap rock and the fracturing pressure should not be exceeded for each gas separately.Other values of capillary threshold pressure for CO₂ and H₂ significantly affect the amount of a given gas that can be injected into the reservoir. The structure under consideration can store approximately 1 Mt CO₂ in 31 years, while in the case of H₂ it is slightly above 4000 tons. The determined CO₂ storage capacity is limited; the structure seems to be more prospective for underground H₂ storage. The CO₂ and H₂ dynamic storage capacity maps are an important element of the analysis of the use of gas storage structures. A much higher fingering effect was observed for H₂ than for CO₂, which may affect the withdrawal of hydrogen. It is recommended to determine the optimum storage depth, particularly for hydrogen. The presented results, important for the assessment of the capacity of geological structures, also relate to the safety of use of CO₂ and H₂ underground storage space.     

Underground hydrogen storage to balance seasonal variations in energy demand: Impact of well configuration on storage performance in deep saline aquifers

Grid-scale underground hydrogen storage (UHS) is essential for the decarbonization of energy supply systems on the path towards a zero-emissions future. This study presents the feasibility of UHS in an actual saline aquifer with a typical dome-shaped anticline structure to balance the potential seasonal mismatches between energy supply and demand in the UK domestic heating sector. As a main requirement for UHS in saline aquifers, we investigate the role of well configuration design in enhancing storage performance in the selected site via numerical simulation. The results demonstrate that the efficiency of cyclic hydrogen recovery can reach around 70% in the short term without the need for upfront cushion gas injection. Storage capacity and deliverability increase in successive storage cycles for all scenarios, with the co-production of water from the aquifer having a minimal impact on the efficiency of hydrogen recovery. Storage capacity and deliverability also increase when additional wells are added to the storage site; however, the distance between wells can strongly influence this effect. For optimum well spacing in a multi-well storage scenario within a dome-shaped anticline structure, it is essential to attain an efficient balance between well pressure interference effects at short well distances and the gas uprising phenomenon at large distances. Overall, the findings obtained and the approach described can provide effective technical guidelines pertaining to the design and optimization of hydrogen storage operations in deep saline aquifers.     

Toward underground hydrogen storage in porous media: Reservoir engineering insights

Subsurface hydrogen storage in depleted hydrocarbon reservoirs and saline formations is a potential option for storing hydrogen at large scales. These subsurface formations need to store sufficient hydrogen efficiently and securely, and the hydrogen must be withdrawn in adequate quantities on demand. In this study, we investigate the reservoir, geological, and operational controls that enable large-scale hydrogen storage and maximize hydrogen injection and withdrawal from depleted natural gas reservoirs. Hydrogen injection, storage, and withdrawal scenarios were computed using a reservoir simulator. Sensitivity analyses exposed the crucial parameters to achieve the goal of optimum storage and withdrawal of hydrogen. We determined that reservoirs with smaller pressures at the start of storage operations are suitable for hydrogen storage if wellhead pressure constraints permit. Steeply dipping reservoirs enable better hydrogen withdrawal if the reservoirs have good permeability (greater than 100 mD) and the injection/withdrawal well is placed updip within the reservoir. Permeable reservoirs and reservoirs with sufficient thickness increase hydrogen withdrawal rates. These findings and the results of the sensitivity analyses are used to propose site selection criteria for underground storage of hydrogen in depleted gas reservoirs.     

Development of a novel simulator for modelling underground hydrogen and gas mixture storage

Underground hydrogen storage can store grid-scale energy for balancing both short-term and long-term inter-seasonal supply and demand. However, there is no numerical simulator which is dedicated to the design and optimisation of such energy storage technology at grid scale. This study develops novel simulation capabilities for GPSFLOW (General Purpose Subsurface Flow Simulator) for modelling grid-scale hydrogen and gas mixture (e.g., H₂–CO₂–CH₄–N₂) storage in cavern, deep saline aquifers and depleted gas fields.The accuracy of GPSFLOW is verified by comparisons against the National Institute of Standard and Technology (NIST) online thermophysical database and reported lab experiments, over a range of temperatures from 20 to 200 °C and pressure up to 1000 bar. The simulator is benchmarked against an existing model for modelling pure H₂ storage in a synthetic aquifer. Several underground hydrogen storage scenarios including H₂ storage in a synthetic salt cavern, H₂ injection into a CH₄-saturated aquifer experiment, and hydrogen storage in a depleted gas field using CO₂ as a cushion gas are used to test the GPSFLOW's modelling capability. The results show that GPSFLOW offers a robust numerical tool to model underground hydrogen storage and gas mixture at grid scale on multiple parallel computing platforms.     

Geochemical reactions-induced hydrogen loss during underground hydrogen storage in sandstone reservoirs

Underground hydrogen storage (UHS) appears to be an important means as a large-scale and long-term energy storage solution. A primary concern of UHS is the in-situ geochemical reactions-induced hydrogen loss. In this context, we performed geochemical modelling to examine the hydrogen loss associated with hydrogen dissolution and fluid-rock interactions using PHREEQC (Version 3) as a function of temperature and pressure. We also performed geochemical modelling with kinetics to investigate the potential hydrogen loss in two commercial gas storage reservoirs (Tubridgi and Mondarra) in Western Australia against the reservoir mineralogy, fluid properties, depth and temperature.Our results show that increasing pressure and temperature only slightly increases hydrogen solubility in brines without minerals. Increasing salinity slightly decreases the solubility of hydrogen in brines. The saturated hydrogen aqueous solution almost does not react with silicate and clay minerals, which is favorable for underground hydrogen storage in quartz-rich sandstone reservoirs. However, unlike silicate and clay minerals, carbonates like calcite triggers up to 9.5% hydrogen loss due to calcite dissolution induced hydrogen dissociation process. Kinetic simulations show that Tubridgi only leads to 0.72% of hydrogen loss, and Mondarra causes 2.76% of hydrogen loss as a result of reservoir calcite dissolution and hydrogen dissociation in brines in 30-year time. Nearly over 87% of calcite cement from Mondarra may be dissolved in 30-year, suggesting potential risks associated with wellbore stability. In conclusion, geochemical reactions-induced hydrogen loss would be minor for UHS in porous media, and we argue that deep calcite-free reservoirs together with calcite-free caprocks would be preferable for underground hydrogen storage.     

The implications of fingering in underground hydrogen storage

Although underground storage in aquifers appears to be the most promising option for large-scale storage of hydrogen, unstable flow which leads to fingering will present limitations to economical operation because it increases losses. For example, the rate of solution of gas into ground water is accelerated due to the increase in surface area of the underground gas bubble. The dimensions of fingers are discussed and experiments with laboratory models are interpreted to indicate how an underground gas bubble develops: an initially circular gas bubble grows fingers which split and branch out forming a tree-like structure. Cushion gas will be a major expense of underground hydrogen storage. It may be possible to use a gas other than hydrogen as the cushion; however, fingering will again provide limitations.     

Comprehensive study of the underground hydrogen storage potential in the depleted offshore Tapti-gas field

Hydrogen is becoming an alternative for conventional energy sources due to absence of any Greenhouse Gases (GHG) emissions during its usage. Geological storage of hydrogen will be potential solution for dealing with large volume requirement to manage uninterrupted Hydrogen supply-chain. Geological Storages such as depleted reservoirs, aquifers and salt caverns offer great potential option for underground hydrogen storage (UHS). There are several depleted gas fields in India. One of such field is located in Tapti-Daman formation. A comprehensive study is conducted to assess the possibility of hydrogen storage in this Indian field which is first of its kind. The geological characteristic of this site is assessed for its viability for storage. Additionally, several aspects including storage capacity, sealability, chemical and micro-biological stability, reservoir simulation, and production viability are assessed using various analytical and numerical models.The qualitative analysis of the Tapti-gas field suggests that the integrity of the storage site will be intact due to existing anticlinal four-way closed structure. The chemical and micro-biological losses are minimal and will not lead to major loss of hydrogen over time. The reservoir modeling results show that optimum gas production-injection scheme needs to be engineered to maintain the required reservoir pressure level in the Tapti-gas field. Also, the deliverability of the various seasonal storage time show that 80 days production scheme will be suitable for efficient operation in this field. Finally, a synergistic scheme to enable green energy production, storage, and transportation is proposed via implementation of UHS in the offshore Tapti-gas field.     

Assessment of feasible strategies for seasonal underground hydrogen storage in a saline aquifer

Renewable energies fluctuate, resulting in temporary mismatches between demand and supply. The conversion of surplus energy to hydrogen and its storage in geological formations is one option to counteract this energy imbalance. This study evaluates the feasibility of seasonal storage of hydrogen produced from wind power in Castilla-León region (northern Spain). A 3D multiphase numerical model is used to test different extraction well configurations during three annual injection-production cycles in a saline aquifer. Results demonstrate that underground hydrogen storage in saline aquifers can be operated with reasonable recovery ratios. A maximum hydrogen recovery ratio of 78%, which represents a global energy efficiency of 30%, has been estimated. Hydrogen upconing emerges as the major risk on saline aquifer storage without using other cushion gases. However, shallow extraction wells can minimize its effects. Steeply dipping geological structures are key for an efficient hydrogen storage.     

A detailed comparative performance study of underground storage of natural gas and hydrogen in the Netherlands

With the expected increase in the use of hydrogen as an energy carrier, large-scale underground storage sites will be needed. Unlike underground natural gas storage (UGS), many aspects on the performance of underground hydrogen storage (UHS) are not well understood, as there is currently no UHS in use for energy supply. Here we present the results of a detailed comparative performance study of UGS and UHS, based on an inflow/outflow nodal analysis. Three UGS sites in depleted gas fields and one in a salt cavern cluster in the Netherlands are used as case studies. The results show that although hydrogen can be withdrawn/injected at higher rates than natural gas, this can be limited by technical constraints. It also indicates that wider ranges of working pressures are required to increase the storage capacity and flow performance of an UHS site to compensate for the lower energy density of hydrogen.     

Hydrogen underground storage—Petrographic and petrophysical variations in reservoir sandstones from laboratory experiments under simulated reservoir conditions

Fluctuating energy production by renewables is one of the main issues in transition times of energy production from conventional power plants to an energy production by renewables. Using excess produced electricity (windy/sunny periods) to convert water to oxygen and hydrogen and storing the hydrogen in depleted oil-, gas fields or sedimentary aquifer structures would provide the option to recover and convert hydrogen to electricity in periods with an energy demand. Research focus is here the pore space in the geological underground where still few studies exist. In static batch experiments up to six weeks long, under different reservoir-specific conditions; regarding pressure, temperature and formation fluid salinity, sandstones were exposed to 100% hydrogen. Before and after these experiments microscopic, petrophysical and computer tomography analyses are conducted. The preliminary results from different scales (μm to cm) and dimensions (2D and 3D) of 21 samples indicate that hydrogen underground storage is likely possible.     

Pore scale investigation of hydrogen injection in sandstone via X-ray micro-tomography

The challenge associated with large-scale hydrogen storage is a pertinent one to achieve a hydrogen economy. The increasing global demand for clean and green energy is the driving force to propel such an economy. Furthermore, hydrogen is also considered an alternative energy source compared to fossil fuel as a clean energy alternative. Hydrogen geo-storage in a deep saline aquifer, depleted oil and gas reservoirs can resolve this challenge. We assess the potential of a saline aquifer in a sandstone formation to store hydrogen through first-of-its-kind x-ray micro-computed tomography miniature coreflood experiments. The investigation shows that ~65% of the sandstone's pore volume can be occupied by hydrogen when injected at a slow rate. Residual saturation of hydrogen upon brine injection can be ~41%.     

Salt domes in Poland – Potential sites for hydrogen storage in caverns

Salt bearing formations have world-wide distribution. The geological structures of Permian salt bearing deposits in Poland are similar to those in the other parts of the Central European salt basin, to which they belong as its SE part. There is a notable trend to use salt domes as sites for underground storage of various gases, fuels and other substances, including hydrogen. Possibilities of using salt domes in Poland for underground hydrogen storage are presented with the focus on the option of using the underground space for energy storage. Usefulness of the 27 hitherto studied salt domes in the Polish Lowlands for underground hydrogen storage in caverns is evaluated using analytical methods of the geology of mineral deposits.Seven not yet developed salt domes are selected as the most promising ones, taking into account geological and reservoir criteria: Rogó?no, Damas?awek, Lubień, ?ani?ta, Goleniów, Izbica Kujawska and D?bina. Initial experience in underground hydrogen storage in salt caverns is presented. Geological conditions favourable for hydrogen storage in underground caverns leached in salt domes are outlined. Their advantage relative to underground storage sites in porous rocks (depleted hydrocarbon deposits and deep aquifers) is discussed.     

Blasingame decline theory for hydrogen storage capacity estimation in shale gas reservoirs

The estimation of storage capacity is crucial for underground hydrogen storage. Shale gas reservoirs have low permeability and porosity, so it is the potential site for hydrogen storage. The study is based on the depleted shale gas reservoirs with multiple flow mechanisms (diffusion, desorption and seepage). Firstly, this paper, using Laplace transformation, point source function and Stehfest inversion, presents a semi-analytical solution for bottom-hole pressure response with hydrogen duration injection. Then we, considering the multiple flow mechanisms, deduce a material balance equation specifically for shale gas reservoirs and plot modified type curves based on the Blasingame decline analysis theory. Furthermore, we discuss the effects of different critical parameters related to hydrogen storage capacity on type curves. In the final part, we describe in detail the method of obtaining hydrogen reserves using type curves. The proposed one can estimate the hydrogen volume in fractures and matrix systems, and get the actual underground storage volume through pressure response, compared with the hydrogen storage capacity calculated by the volumetric method. This study is helpful for the hydrogen capacity estimation of shale gas underground storage on-site.     

Assessment of the potential for underground hydrogen storage in bedded salt formation

Salt formations of an appropriate thickness and structure, common over the globe, are potential sites for leaching underground caverns in them for storage of various substances, including hydrogen. Underground hydrogen storage, considered as underground energy storage, requires, in first order, an assessment of the potential for underground storage of this gas at various scales: region, country, specific place.The article presents the results of the assessment of the underground hydrogen storage potential for a sample bedded salt formation in SW Poland. Geological structural and thickness maps provided the basis for the development of hydrogen storage capacity maps and maps of energy value and heating value. A detailed assessment of the hydrogen storage capacity was presented for the selected area, for a single cavern and for the cavern field; a map of the energy value of stored hydrogen has also been presented. The hydrogen storage potential of the salt caverns was related to the demand for electricity and heat. The results show the huge potential for hydrogen storage in salt caverns.     

压缩空气地下咸水含水层储能技术

能源危机和温室效应促进了可再生能源的利用,储能技术是解决太阳能、风能波动问题的重要手段。压缩空气储能（Compressed Air Energy Storage, CAES）技术是仅次于抽水蓄能的第二大蓄能技术。目前CAES多是通过洞穴实现,其主要缺点是对地质要求较高,合适的洞穴数量有限,为扩大其应用,可使用地下咸水含水层作为储层。本文介绍了CAES电站的工作原理、优缺点及各国的发展现状,并分析了利用地下咸水含水层进行压缩空气储能的可行性、优点及一些问题与技术方法,如储层内残余烃的影响、氧化与腐蚀作用、颗粒的影响及缓冲气的选择,表明含水层CAES将是拓宽CAES应用的重要途径。     

Study on underground thermal characteristics by using digital national land information, and its application for energy utilization

This paper describes a method for evaluating characteristics of underground thermal properties and groundwater, whose evaluation is essential for designing systems of underground thermal energy utilization. First, the systems using underground thermal energy are classified into two categories: borehole system with indirect heat exchange, and aquifer system with direct use of underground water. These systems are also divided into thermal storage systems and heat source/sink systems. Second, the characteristics of the underground in Japan are analyzed by using a geographical information system (GIS) and hydrogeological information. Regulations on environmental protection, such as those relating to national parks for instance, and the distribution of thermal energy demand eliminate 77% of Japan from consideration for underground thermal energy utilization. Areas limited to borehole thermal energy utilization account for 17% of areas where underground thermal energy can be used, with the remaining 74% suitable for both boreholes and aquifers. Finally, we estimate the thickness of aquifer and groundwater velocity in Sapporo. We find that most parts of Sapporo are suitable for aquifer thermal energy storage (ATES).     

Screening and ranking framework for underground hydrogen storage site selection in Poland

This paper proposes the use of the Analytic Hierarchy Process (AHP) in order to select the potential underground hydrogen storage sites. The preliminary selection and evaluation of hydrogen storage sites may be considered as a multi-criteria decision-making process. The use of a decision model based on 5 (for aquifers) or 6 geological criteria (in the case of salt and hydrocarbon deposits) has been proposed. A ranking of salt structures, aquifers, and crude oil and natural gas reservoirs, previously identified as the potential hydrogen storage sites in Poland, has been presented. The obtained results have confirmed that the AHP-based approach can be useful for preliminary selection of potential underground hydrogen storage sites. The proposed method enables one to objectively choose the most satisfactory decision, from the point of view of the adopted decision-making criteria, regarding the choice of the best structure.     

Hydrogen storage in saline aquifers: The role of cushion gas for injection and production

Hydrogen stored on a large scale in porous rocks helps alleviate the main drawbacks of intermittent renewable energy generation and will play a significant role as a fuel substitute to limit global warming. This study discusses the injection, storage and production of hydrogen in an open saline aquifer anticline using industry standard reservoir engineering software, and investigates the role of cushion gas, one of the main cost uncertainties of hydrogen storage in porous media.The results show that one well can inject and reproduce enough hydrogen in a saline aquifer anticline to cover 25% of the annual hydrogen energy required to decarbonise the domestic heating of East Anglia (UK). Cushion gas plays an important role and its injection in saline aquifers is dominated by brine displacement and accompanied by high pressures. The required ratio of cushion gas to working gas depends strongly on geological parameters including reservoir depth, the shape of the trap, and reservoir permeability, which are investigated in this study. Generally, deeper reservoirs with high permeability are favoured. The study shows that the volume of cushion gas directly determines the working gas injection and production performance. It is concluded that a thorough investigation into the cushion gas requirement, taking into account cushion gas costs as well as the cost-benefit of cushion gas in place, should be an integral part of a hydrogen storage development plan in saline aquifers.     

地下咸水层水-热-盐耦合模型及其储能利用研究

基于地下水水热运移的基本原理,针对地下咸水层储能系统中地下水密度及粘滞性系数变化显著的特点,建立地下咸水层水-热-盐耦合储能模型。应用校正后的数学模型,对天津滨海某地下咸水层储能系统未来5 a的地下水动力场和温度场的变化进行了预测。结果表明:在地下咸水层水文地质条件不变的情况下,渗透系数随地下咸水层温度和浓度的增减而增减;在夏季储热期,地下水渗透流速随地下温度的上升呈逐渐上升趋势;在冬季储冷期,地下水渗透流速随地下水温度的下降呈逐渐下降趋势,从而影响地下咸水层温度场的变化,在第5年供冷期末,3#抽水井水温上升0.5℃,发生热突破现象。     

Temperature and pressure variations within compressed air energy storage caverns

In the present work, the thermodynamic response of underground cavern reservoirs to charge/discharge cycles of compressed air energy storage (CAES) plants was studied. During a CAES plant operation, the cyclical air injection and withdrawal produce temperature and pressure fluctuations within the storage cavern. Predictions of these fluctuations are required for proper cavern design and for the selection of appropriate turbo-machinery. Based on the mass and energy conservation equations, numerical and approximate analytical solutions were derived for the air cavern temperature and pressure variations. Sensitivity analyses were conducted to identify the dominant parameters that affect the storage temperature and pressure fluctuations and the required storage volume. The heat transfer at the cavern walls was found to highly affect the air temperature and pressure variations as compared to adiabatic conditions. In essence, heat transfer reduces the temperature and pressure fluctuations during cavern charge and discharge and effectively leads to a higher storage capacity. Additionally, for realistic conditions, in each cycle, few percents of the injected energy are lost by conduction into the rocks. The principal thermal property that governs the heat transfer process is the rock effusivity. To reduce the required storage volume preference must be given to sites of rocks that have the largest thermal effusivity. Lower injected air temperatures also reduce the required storage volume, but increase the cooling costs. The injected temperature can also be used to control the cycle temperature extreme limits. It is evident from the results that the storage pressure ratio has a dominant effect on the required storage volume and should preferably range between 1.2 and 1.8.